Invoking the Tnm::dns
command with options but without any command arguments allows retrieving
and changing the default values. Default values are bound to a Tcl interpreter,
which allows having multiple Tcl interpreters with different defaults.

The Tnm::dns name
command sends a query to retrieve the domain name pointer record. A pointer
record maps an IP address to a fully qualified domain name. The command
returns the fully qualified domain name for the given IP address.

The Tnm::dns hinfo
command sends a query to retrieve the host information (HINFO) record.
The command returns a list containing two elements. The first element describes
the hardware type and the second element the operating system.

The Tnm::dns mx
command sends a query to retrieve the mail exchanger (MX) record. The command
returns a list of mail exchanger records if name is a domain name for which
one or more MX records exist. Each element of this list contains a fully
qualified domain name and its priority.